CONCENTRIC CAMSHAFT WITH ELECTRIC PHASE DRIVE

FIELD OF THE INVENTION

[0001] The present invention relates to a concentric camshaft with electric phase drive. More specifically, the present invention relates to a concentric camshaft with electric phase drive for altering the phasing of the timing of valves actuated by the concentric camshaft.

BACKGROUND OF THE INVENTION

[0002] Variable valve timing is now increasingly employed with internal engines to improve their fuel efficiency and/or performance. In conventional internal combustion engines, the angular positions of the cam lobes actuating the valves of the engine are fixed with respect to the angular position of the crankshaft, the camshaft being rotated at precisely one-half the speed of the crankshaft by a synchronous drive. Thus, the valves of the engine always open and close at the same position with respect to the position of their respective pistons.

[0003] In an engine with variable valve timing, the angular position of the cam lobes can be altered, with respect to the angular position of the crankshaft, thus allowing the valves to be opened and/or closed sooner or later with respect to a given piston position.

[0004] When the internal combustion engine employs separate cams to operate the inlet valves and the exhaust valves, the timing between the opening and closing of the inlet and exhaust valves, relative to each other, can also be altered and this is typically referred to as variable valve phasing. Specifically, in variable valve phasing the angular position of the inlet valve camshaft, relative to the crankshaft, can be altered independently of the angular position of the exhaust camshaft, relative to the crankshaft. The difference between the angular positions of the camshafts to the crankshaft is typically referred to as the "phase" of the valves and the drive mechanisms which advance or retard the angular position of the camshafts relative to the crankshaft are typically referred to as phase drives.

[0005] Generally, the phase drive operates between a drive pulley, attached to a synchronous drive driven by the engine crankshaft, and the camshaft. In most cases, the phase drives are operated by a supply of pressurized lubrication oil which is modulated, as need, by a valve timing controller to alter the angular position of the

camshaft relative to the drive pulley and thus relative to the crankshaft. Typically, increasing the supply of pressurized lubrication fluid advances the angular position of a cam relative to the drive pulley and decreasing the supply of pressurized lubrication fluid retards the angular position of a cam relative to the drive pulley. [0006] While such variable valve phasing offers numerous improvements to the operation of an engine, it still suffers from some disadvantages. In particular, engines do not typically have a sufficient available supply of pressurized lubricating oil when they are being started and/or at low operating speed, and thus valve phase drives cannot be operated as desired.

[0007] One attempt to deal with this issue is described in published U.S. Patent 2006/0260573 to Urushihata et al. In this reference, a planetary gear is placed between an outer gear on the drive pulley and an inner gear driving the camshaft. The planetary gear is rotatably mounted to a drive shaft which can, in turn, be rotated by an electric motor. Rotation of the planetary gear by the electric motor changes the speed of rotation of the inner gear, relative to the outer gear, to advance or retard the angular position of the camshaft with respect to the drive pulley. As the electric motor is operated independently of a supply of pressurized lubrication oil, the valve timing can be set, as desired, even at start up and at low operating speeds of the engine. [0008] However, more recently variable valve phasing systems have been developed for engines which employ a camshaft that has lobes to operate both inlet and exhaust valves. Camshafts for such systems are generally referred to as concentric camshafts, or concentric phasing camshafts, and typically include a concentrically arranged outer member and inner member. A set of lobes operating, either the inlet or exhaust valves, is mounted to the outer member and a set of lobes operating the other of the inlet and exhaust valves is mounted to the inner member via pins into the inner member which pass through slots in the outer member. A phase drive mechanism, such as that described in U.S. Patent 6,725,817 to Methley et al., can alter the relative angular positions of the inner and outer members to change the valve phasing as needed. [0009] While such concentric camshafts provide the benefits of variable valve timing to engines with camshafts that operate both inlet and exhaust valves, to date systems employing concentric camshafts have only been operable with phase drives operated from pressurized lubricating oil, such as taught by the Methey reference, and have suffered from the problems, described above, at engine start time and/or at low engine

operating speeds. While the Urushihata development appears to be an improvement over the prior art phase drives operated solely by pressurized lubrication oil, the Urushihata development cannot be employed with concentric camshaft systems.

SUMMARY OF THE INVENTION

[0010] It is an object of the present invention to provide a novel concentric camshaft with electric phase drive and a method of operating such a drive which obviates or mitigates at least one disadvantage of the prior art.

[0011] According to a first aspect of the present invention, there is provided a concentric camshaft and electric phase drive system, comprising: an outer camshaft member having at least one cam lobe affixed to it; an inner camshaft member rotatably mounted with the outer camshaft member and having at least one cam lobe affixed to it by a member extending from the at least one cam lobe through a slot in the outer camshaft member and into the inner camshaft member; a drive sprocket to receive a synchronous drive to rotate the outer camshaft member and the inner camshaft member; and an electric phase drive independently acting between the drive sprocket and each of the inner camshaft member and the outer camshaft member and operable to advance and/or retard the angular position of the inner camshaft member relative to the angular position of the drive sprocket and to advance and/or retard the angular position of the outer camshaft member relative to the angular position of the drive sprocket.

[0012] The present invention provides a novel concentric camshaft with electric phase drive which allows the angular position of a first set of cam lobes to be advanced or retarded with respect to the angular position of a drive sprocket and which allows the angular position of a second set of cam lobes to be advanced or retarded with respect to the angular position of the drive sprocket, the advancement or retardation of the first and second sets of cam lobes being independent of each other. Further, the electric phase drive permits the advancement and retardation of the sets of cam lobes to be performed, as desired, independently of the operating speed or condition of the engine in which the concentric camshaft is installed.

BRIEF DESCRIPTION OF THE DRAWINGS

[0013] Preferred embodiments of the present invention will now be described, by way of example only, with reference to the attached Figures, wherein:

Figure 1 shows a schematic representation of a concentric camshaft with electric phase drive in accordance with the present invention;

Figure 2 shows a schematic representation of another drive mechanism for use with a concentric camshaft of the present invention;

Figure 3 shows a schematic representation of another concentric camshaft with electric phase drive in accordance with the present invention;

Figure 4 shows a schematic representation of another concentric camshaft with electric phase drive in accordance with the present invention;

Figure 5 shows a schematic representation of another concentric camshaft with electric phase drive in accordance with the present invention;

Figure 6 shows a schematic representation of another concentric camshaft with electric phase drive in accordance with the present invention; and

Figure 7 shows a schematic representation of another drive mechanism for use with a concentric camshaft of the present invention.

DETAILED DESCRIPTION OF THE INVENTION

[0014] A concentric camshaft and electric phase drive system, in accordance with the present invention, is indicated generally at 20 in Figure 1. [0015] As shown, system 20 comprises a multipart camshaft 24 which includes at least one outer cam lobe 28 attached to an outer tubular member 32 of camshaft 24 and at least one inner cam lobe 36 attached by a pin 40, to an inner tubular member 44 of camshaft 24. As can be seen, pin 40 extends through inner member 44 and through a slot 48 in outer member 32 such that the angular position of cam lobe 36 can be changed with respect to the angular position of outer member 32, as described below in more detail.

[0016] While only a single cam lobe 28 is shown attached to outer member 32, it should be apparent to those of skill in the art that cam lobe 28 is intended to represent one of a set of either exhaust or inlet cams of an engine in which system 20 is installed. Similarly, while only a single cam lobe 36 is shown attached to inner member 44, it should be apparent to those of skill in the art that cam lobe 36 is intended to represent the other of the sets of either exhaust or inlet cams of an engine in which system 20 is installed.

[0017] Camshaft 24 is rotated by a drive sprocket 52 which is driven by the crankshaft of an engine by a synchronous drive (not shown) and rotates on a support

bearing 54. A first control shaft 56 extends from a control yoke 60 through drive sprocket 52 and into one end of outer member 32. A portion of the outer surface of first control shaft 56 includes a set of splines 64 which engage a complementary set of splines on drive sprocket 52 such that first control shaft 56 rotates with drive sprocket 52 but is also free to move toward or away from camshaft 24 in response to movements of control yoke 60.

[0018] The end of first control shaft 56 which extends into the end of outer member 32 includes a helical groove 68 which is complementary to another helical groove (not illustrated) formed in the interior of outer member 32 and one or more ball bearings (not shown) ride in the passage formed by the two helical grooves such that movement of first control shaft 56 towards and/or away from outer member 32 results in rotation of outer member 32 (and cam 28) about first control shaft 56. Thus, as should now be apparent, the angular position of cam 28, with respect to the angular position of drive sprocket 52, can be varied by moving control yoke 60 and first control shaft 56 towards or away from camshaft 24, while still allowing torque from drive sprocket 52 to be transferred to cam lobe 28.

[0019] As illustrated, first control shaft 56 is hollow and a second control shaft 72 extends from a second control yoke 76, through first control shaft 56, and into one end of inner member 44. A portion of the outer surface of second control shaft 72 includes a set of splines (not illustrated) that engage a complementary set of splines on a portion of the interior of first control shaft 56 such that second control shaft 72 rotates with first control shaft 56 and drive sprocket 52 but is also free to move toward or away from camshaft 24 in response to movements of control second yoke 76. [0020] Similar to first control shaft 56, the end of second control shaft 72 which extends into the end of inner member 44 includes a helical groove 80 which is complementary to another helical groove (not illustrated) formed in the interior of inner member 44 and one or more ball bearings (not shown) ride in the passage formed by the two helical grooves such that movement of second control shaft 72 towards and/or away from inner member 44 results in rotation of inner member 44 (and cam 36) about second control shaft 72. Thus, as should now be apparent, the angular position of cam 36, with respect to the angular position of drive sprocket 52, can be varied by moving second control yoke 76 and second control shaft 72 toward or away from camshaft 24, while still allowing torque from drive sprocket 52 to be transferred to cam lobe 36.

[0021] While the illustrated embodiment employs a set complementary helical grooves with one or more ball bearings to connect first control shaft 56 to outer member 32 and second control shaft 72 to inner member 32 it will be apparent to those of skill in the art that the present invention is not so limited and any suitable mechanism, as would occur to those of skill in the art, which can convert lateral movement of a control shaft into an angular displacement of a camshaft member can be employed. [0022] It is further contemplated that, to reduce play between first control shaft 56 and outer member 32 a torsion spring 84 can be included to bias outer member 32 to a fully advanced or fully retarded position with respect to first control shaft 56. Similarly, to reduce play between second control shaft 72 and inner member 44 a torsion spring 88 can be included to bias inner member 44 to a fully advanced or fully retarded position with respect to second control shaft 72.

[0023] Control yoke 60 can be positioned by any suitable actuator or control means, and in the illustrated embodiment, is positioned by a stepper motor 92 and a linear screw 96. Similarly, second control yoke 76 can be positioned by any suitable control means, and in the illustrated embodiment, is positioned by a stepper motor 100 and a linear screw 104. Each of stepper motors 92 and 100 can be controlled by any suitable control mechanism, such as an engine control unit (ECU) which provides power 108 to motors 92 and 100, and can include position sensors 1 12 which provide appropriate feedback signals to control mechanism to indicate the position, in advance or retardation, of cams 28 and 36 relative to the angular position of drive sprocket 52. [0024] As should now be apparent to those of skill in the art, by employing stepper motors 92 and 100, the inlet and exhaust cams of camshaft 24 can be set to any desired degree of angular advance or retardation, with respect to drive sprocket 52, independent of whether the engine in which system 20 is installed is running and/or independent of the operating speed of the engine.

[0025] Figure 2 shows another drive mechanism for a second embodiment of the present invention wherein like components to those of Figure 1 are identified with like reference numerals. In this embodiment, control yoke 60 and second control yoke 76 and their related components have been replaced with an electro-mechanical drive mechanism 200. Specifically, drive mechanism 200 comprises a first armature 204 which is fixed to, and rotates with, first control shaft 56 and a second armature 208 which is fixed to, and rotates with, second control shaft 72. Drive mechanism 200

further comprises a stator 212, which is stationary and fixed via one or more mounts 216 to the engine in which system 20 is installed. Each of armatures 204 and 208 are biased away from stator 212 by biasing springs (not shown). [0026] Stator 212 includes two, independently operable, electro magnetic coils 220 and 224 and further includes a pair of suitable sensors (not shown) which output a signal representative of the distance of armature 204 from stator 212 and a signal representative of the distance of armature 208 from stator 212. [0027] As should now be apparent to those of skill in the art, by controlling the voltage and polarity of the power (and hence the current) applied to coil 224, armature 204 can be moved toward or away from stator 212, thus moving first control shaft 56 toward or away from outer member 32. Similarly, by controlling the voltage and polarity of the power applied to coil 220, armature 208 can be moved toward (by increasing the current) or away from stator 212 (by decreasing the current), thus moving second control shaft 72 toward or away from outer member 32. A suitable control mechanism, such as an ECU or embedded processor unit, receives the signals relating to the distances of each of armatures 204 and 208 from stator 212 and supplies appropriate current levels and polarities to each of coils 220 and 224 to control the advance and/or retardation of the inlet and exhaust cam lobes of camshaft 24 relative to the angular position of drive sprocket 52.

[0028] Again, as drive mechanism 200 does not require a supply of pressurized lubrication oil, the inlet and exhaust cams of camshaft 24 can be set to any desired degree of angular advance or retardation, with respect to drive sprocket 52, independent of whether the engine in which system 20 is installed is running and/or independent of the operating speed of the engine.

[0029] Figure 3 shows another embodiment of a concentric camshaft and electric phase drive system 300 of the present invention wherein like components to those of Figure 1 are identified with like reference numerals. In Figure 3, helical grooves 68 and 80 have been omitted from the Figure for clarity.

[0030] In system 300, torsion springs 80 and 84 generate sufficient force to fully advance both outer member 32 and inner member 44, with respect to the angular position of drive sprocket 52, even when the engine in which system 300 is installed is operating.

[0031] To retard outer member 32 from the fully advanced position to a neutral position or to a retarded position, a rotor 304 is fixed to first control shaft 56 and rotor 304 passes through a brake coil 308 which operates as an eddy current, or hysteresis coil. When an electric current 312 is applied to brake coil 308, a brake force is applied to rotor 304 and this brake force acts against the bias force of torsion spring 84 to retard the angular position of outer member 32, and cam lobe 28, from the fully advanced position. By controlling the electrical current applied to brake coil 308, the amount of brake force applied to rotor 304 can be controlled and the angular position of outer member 32 and cam lobe 28 selected as desired.

[0032] Similarly, a rotor 316 is fixed to second control shaft 72 and rotor 316 passes through a brake coil 320. When an electric current 324 is applied to brake coil 320, a brake force is applied to rotor 320 and this brake force acts against the bias force of torsion spring 88 to retard the angular position of inner member 44, and cam lobe 36, from the fully advanced position. By controlling the electrical current applied to brake coil 320, the amount of brake force applied to rotor 316 can be controlled and the angular position of inner member 44 and cam lobe 36 selected as desired. [0033] In order to control system 300, it is contemplated that a sensor 328 will provide a signal indicative of the angular position of drive sprocket 52. Similarly, a sensor 332 can provide a signal representative of the angular position of rotor 304 and a sensor 336 can provide a signal representative of the angular position of rotor 316. Each of these sensor output signals can be applied to a control device, such as an ECU which can control the current supplied to brake coils 308 and 320 as appropriate to obtain the desired advance or retardation of outer member 32 and inner member 44. [0034] Figure 4 shows another embodiment of a concentric camshaft and electric phase drive system 400 of the present invention wherein like components to those of Figure 1 are identified with like reference numerals.

[0035] In system 400, first control shaft 56 is fixed to outer member 32 such that outer member 32 turns with first control shaft 56. Similarly, second control shaft 72 is fixed to inner member 44 such that inner member 44 turns with second control shaft 72. Unlike the earlier embodiments discussed above, in system 400 drive sprocket 52 does not inter-engage first control shaft 56 via a set of splines. Instead, a lost motion connection is utilized wherein the drive sprocket 52 includes a stop 404 which can engage either end of a slot 408 in first control shaft 56 and, within the limits created by

stop 404 and the ends of slot 408, first control shaft 56 is free to rotate independently of drive sprocket 52 for a portion of one revolution.

[0036] While not shown in the figure, first control shaft 56 includes a similar stop to stop 404 which extends radially inwardly into a slot, similar to slot 408, formed in second control shaft 72 such that, within the limits created by this stop and the ends of this slot, second control shaft 72 is free to rotate independently of first control shaft 56 and drive sprocket 52.

[0037] First control shaft 56 is connected to a drive motor 412 and second control shaft 72 is connected to a second drive motor 416. Drive motor 412 serves to rotate first control shaft 56 and outer member 32 when the engine in which system 400 is installed is operating. By altering the rotational speed of motor 416, the angular position of outer member 32, and cam lobe 28, can be set as desired. In the event that drive motor 412 fails, stop 404 engages one end of slot 408 and outer member 32 will rotate with drive sprocket 52 with the angular position of outer member 32 being a failsafe position. Similarly, if drive motor 416 fails, the stop will abut one end of the slot in the interface between first control shaft 56 and second control shaft 72 and inner member 44, and cam lobe 36, will rotate with first control shaft 56 in a failsafe position. [0038] As will be apparent, in normal operating conditions of system 400, drive sprocket 52 acts as an input to a sensor 420 to determine the angular position of the crankshaft of the engine in which system 400 is installed. A control mechanism, such as an ECU, receives the signal from sensor 420, and from a sensor 424 which indicates the angular position of first control shaft 56, and a sensor 428 which indicates the angular position of second control shaft 72. The control mechanism processes these input signals and applies an appropriate electrical input 432, 436 respectively to each of drive motors 412 and 416 to position cam lobes 28 and 36 with the desired angular position relative to the crankshaft.

[0039] Figure 5 shows another embodiment of a concentric camshaft and electric phase drive system 500 of the present invention wherein like components to those of Figure 1 are identified with like reference numerals. System 500 is similar to system 400, except that motor 504 attached to first control shaft 56 is an electric torque motor which acts between a motor mount housing 508 affixed to drive sprocket 52 and first control shaft 56. Similarly, motor 512 attached to second control shaft 72 acts between motor mount housing 508 and second control shaft 72.

[0040] As before, a sensor 516 provides an output signal indicating the angular position of drive sprocket 52, a sensor 520 provides an output signal indicating the angular position of first control shaft 56 and a sensor 524 provides an output signal indicating the angular position of second control shaft 72. Each of these sensor signals is provided to a suitable control mechanism, such as an ECU which alters the electric current 528 and 532 applied, respectively, to motors 504 and 512, via a slip ring commutator 536. By appropriately altering electric current 528 and 532, the angular position of outer member 32 and cam lobe 28 and the angular position of inner member 44 and cam lobe 36 can be set relative to the angular position of drive sprocket 52. [0041] Figure 6 shows another embodiment of a concentric camshaft and electric phase drive system 600 of the present invention wherein like components to those of Figure 1 are identified with like reference numerals. In this embodiment, drive sprocket 52 drives a second drive gear 604 which in turn, drives a pair of planetary gears 608 and 612 which are linked by a shaft 616.

[0042] Planetary gear 612 engages a gear 620 fixed to one end of inner member 44 and thus, as drive sprocket 52 is rotated, inner member 44 is rotated with it. However, as shown shaft 616 is rotatably mounted through a member 624. Member 624 has a radially inner portion which is rotatably mounted to a shaft 628 extending from the center of gear 604 and an outer edge which is toothed to engage a first electric drive motor 632.

[0043] As first electric drive motor 632 is rotated in a first direction, member 624 is rotated in a corresponding first direction about shaft 628, moving planetary gears 608 and 612 about the circumference of second drive gear 604 and thus advancing the angular position of gear 620 with respect to the angular position of drive sprocket 52. As is apparent, advancing the angular position of gear 620 also results in the advancement of cam lobe 36.

[0044] As first electric drive motor 632 is rotated in a second, opposite, direction, member 624 is rotated in a corresponding second direction about shaft 628, moving planetary gears 608 and 612 in the opposite direction about the circumference of second drive gear 604 and thus retarding the angular position of gear 620 with respect to the angular position of drive sprocket 52. As is apparent, retarding the angular position of gear 620 also results in the retardation of cam lobe 36.

[0045] Second drive gear 604 also drives a pair of planetary gears 640 and 644 which are linked by a shaft 648. Planetary gear 644 engages a gear 652 fixed to one end of outer member 32 and thus, as drive sprocket 52 is rotated, outer member 32 is rotated with it. However, as shown shaft 648 is rotatably mounted through a member 656. Member 656 has a radially inner portion which is rotatably mounted to shaft 628 and an outer edge which is toothed to engage a second electric drive motor 660. [0046] As second electric drive motor 660 is rotated in a first direction, member 656 is rotated in a corresponding first direction about shaft 628, moving planetary gears 640 and 644 about the circumference of second drive gear 604 and thus advancing the angular position of gear 652 with respect to the angular position of drive sprocket 52. As is apparent, advancing the angular position of gear 652 also results in the advancement of cam lobe 28.

[0047] As second electric drive motor 660 is rotated in a second, opposite, direction, member 656 is rotated in a corresponding second direction about shaft 628, moving planetary gears 640 and 644 in the opposite direction about the circumference of second drive gear 604 and thus retarding the angular position of gear 652 with respect to the angular position of drive sprocket 52. As is apparent, retarding the angular position of gear 652 also results in the retardation of cam lobe 28. [0048] First electric drive motor 632 is equipped with a sensor 664 which outputs a signal indicating its angular position and second electric drive motor 660 is equipped with similar sensor 670 which outputs a signal indicating its angular position. The signals from sensors 664 and 670 are provided to a suitable control mechanism, such as an ECU or the like, which processes the signals and outputs electric control signals to first electric drive motor 632 and second electric drive motor 660 to advance and/or retard cam lobe 28 and/or cam lobe 36 as desired.

[0049] Figure 7 shows another drive mechanism 700 in accordance with the present invention wherein like components to those of Figure 1 are identified with like reference numerals. In this embodiment, inner member 44 includes an internal ring gear 704 and outer member 32 includes a similar internal ring gear 708.

[0050] Drive sprocket 52 includes a pair of gear shafts 712 and 716 which rotate with drive sprocket 52. A pair of planetary gears 720 and 724 are mounted, respectively, on gear shafts 712 and 716 adjacent drive sprocket 52. Each of planetary gears 720 and

724 engage internal ring gear 708 and a sun gear 728. Sun gear 728 is connected to a phase adjustment sprocket 732 which in turn engages a first electric motor drive 736. [0051] As will now be apparent to those of skill in the art, while sun gear 728 is stationary (i.e. - when first electric motor drive 736 is inactive) outer member 32 will rotate synchronously with drive sprocket 52. To advance or retard the angular position of outer member 32 with respect to the angular position of drive sprocket 52, first electric motor drive 736 is activated to rotate phase adjustment sprocket 732, and thus sun gear 728 and planetary gears 720 and 724. As planetary gears 720 and 724 are rotated, internal ring gear 708 is rotated with respect to drive sprocket 52 and the angular position of outer member 32, relative to drive sprocket 52, is changed. Operating first electric motor drive 736 in one direction will advance the angular position of outer member 32 with respect to drive sprocket 52 and operating first electric motor drive 736 in the opposite direction will retard the angular position of outer member 32 with respect to drive sprocket 52.

[0052] A second pair of planetary gears 740 and 744 are also mounted, respectively, on gear shafts 712 and 716 distal drive sprocket 52. Each of planetary gears 740 and 744 engage internal ring gear 704 and a sun gear 748. Sun gear 748 is connected to a phase adjustment sprocket 752 which in turn engages a second electric motor drive 756.

[0053] As was the case with outer member 32 described above, while sun gear 748 is stationary (i.e. - when second electric motor drive 756 is inactive) inner member 44 will rotate synchronously with drive sprocket 52. To advance or retard the angular position of inner member 44 with respect to the angular position of drive sprocket 52, second electric motor drive 756 is activated to rotate phase adjustment sprocket 752, and thus sun gear 748 and planetary gears 740 and 744. As planetary gears 740 and 744 are rotated, internal ring gear 704 is rotated with respect to drive sprocket 52 and the angular position of inner member 44, relative to drive sprocket 52, is changed. Operating second electric motor drive 756 in one direction will advance the angular position of inner member 44 with respect to drive sprocket 52 and operating second electric motor drive 756 in the opposite direction will retard the angular position of inner member 44 with respect to drive sprocket 52.

[0054] The present invention provides a novel concentric camshaft with electric phase drive which allows the angular position of a first set of cam lobes to be advanced

or retarded with respect to the angular position of a drive sprocket and which allows the angular position of a second set of cam lobes to be advanced or retarded with respect to the angular position of the drive sprocket, the advancement or retardation of the first and second sets of cam lobes being independent of each other. Further, the electric phase drive permits the advancement and retardation of the sets of cam lobes to be performed, as desired, independently of the operating speed or condition of the engine in which the concentric camshaft is installed.

[0055] The above-described embodiments of the invention are intended to be examples of the present invention and alterations and modifications may be effected thereto, by those of skill in the art, without departing from the scope of the invention which is defined solely by the claims appended hereto.